Effect of 3-Isobutyl-1-Methylxanthine on Prolactin Actions on RNA Synthesis, Casein Synthesis, Lipid Synthesis and Ornithine Decarboxylase Activity in Mouse Mammary Gland Explants

Summary The effect of 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of cyclic nucleotide phosphodiesterase, was tested on several actions of prolactin in cultured mouse mammary tissues. At concentrations of 0.5 mM and above, IBMX abolished the actions of prolactin on RNA and casein synthesis. IBMX by itself, stimulated ornithine decarboxylase (ODC) activity in a dose-response fashion; but the IBMX at concentrations up to 1 mM had no effect on the magnitude of the prolactin-stimulated ODC activity. IBMX inhibited in a dose-response fashion the rate of [ 14 C]-acetate incorporation into lipids; however, prolactin stimulated lipid biosynthesis in the presence of IBMX concentrations of up to 1 mM.